1. Field of the Invention
The present invention relates to an optoelectronic device and the method for manufacturing the same and, more particularly, to an optoelectronic device and the method for manufacturing the same, which the optoelectronic effect such as light emission or light reception can be enhanced by forming a dual-structural nano dot to increase the confinement density of electrons and holes.
2. Description of the Prior Art
As application fields of the optoelectronic device, there are a light emitting device, a light receiving device, an optical guide, an optical modulating device, and a spi-LED. Also, as applications using the devices, there are a silicon ULSI, an optical switch, OEIC (Optoelectronic Integrated Circuit) to which optical signals is applied, and an optical computer and a quantum computer circuit to which a solar battery or an optical operation circuit is provided.
Hereinafter, the conventional optoelectronic device using the nano dot will be described with reference to FIG. 1. The general light emitting device has a simple structure which nano dots are formed in silicon or compound semiconductor. In the optoelectronic device in FIG. 1, a hole injection layer 2 is formed on an electron injection layer 1, and the nano dots 6 are formed in hole injection layer 2 near to the interface between the electron injection layer 1 and the hole injection layer 2.
The conventional optoelectronic device has a limitation in that the structures of the energy bands of the nano dot 6 and the electron and hole injection layers 1 and 2 confine carriers. Due to an indirect band gap of the nano dot 6, the efficiency thereof is low. Furthermore, Since the electrons and the holes have not locally confined at the periphery of the nano dots, the carriers are recombined at the interface between the electron injection layer 1 and the hole injection layer 2. It leads the generated light to spread out with undesired wavelength. And, in case where the electron and the hole injection layers are recombined with the indirect transition type, the recombination does not lead to emit the light, so it is transformed into a type of heat energy. Accordingly, the conventional optoelectronic device comes to have a low efficiency, a high leakage current, and low reliability.
To increase the quantum efficiency, the injected minority carriers must be converged to the nano dots when the forward voltage is applied to the PN junction. However, in case where the structure of the energy band of the nano dot is the stagger type, in which the injection and the confinement of the electron and the hole are not accomplished well, the probability of the recombination of the carriers is low. Accordingly, the development of a new device having high quantum efficiency has been required.
Thus, the object of the present invention is to provide us for an optoelectronic device with a structure having the dual-structural nano dots, a small nano dot is formed in a large nano dot, in order to enhance the confinement density of the electrons and the holes, thereby the effective light-emitting and light-receiving operation can be performed.
The another object of the present invention is to provide a method of manufacturing the optoelectronic device.
According to an aspect of the present invention, an optoelectric device comprising an electron injection layer, a nano dot, and a hole injection layer formed in a semiconductor substrate, wherein the nano dot has a dual structure composed of an external nano dot and an internal nano dot is provided.
Preferably, the external nano dot is composed of an indirect transition type semiconductor, and the internal nano dot is composed of a direct transition type semiconductor. The optoelectronic device further comprises a quantum well layer, which is formed between the electron injection layer and the hole injection layer and in which the nano dot is included. In addition, the quantum well layer has a dual structure composed of deep quantum well layers and shallow quantum well layers, the deep quantum well layers are formed adjacent to and symmetric with said nano dot, and the shallow quantum well layer are formed on the upper and the lower portions of the deep quantum well layers, respectively.
As the occasion demands, at least two nano dot layers in which the nano dot are multiply formed.
Preferably, the diameter of the external nano dot is in range of 10 to 100 nm, and the diameter of said internal nano dot is equal to and smaller than 12 nm.
According to the other aspect of the present invention, a method of manufacturing an optoelectric device, comprising the steps of forming an electron injection layer on a semiconductor substrate; growing nano dot layer on the electron injection layer by an epi-growth method; heating the nano dot layer so that the nano dot has a dual structure composed of an external nano dot and an internal nano dot; and forming a hole injection layer on the overall structure is provided.
Preferably, the method may further comprise the step of forming a quantum well layer, before or after the step of growing said nano dot layer, or may further comprise the step of forming an epi-layer to be used as said external nano dot layer, before or after the step of growing said nano dot layer.
In addition, the external nano dot is formed with an indirect transition type semiconductor, and the internal nano dot is formed with a direct transition type semiconductor.
On the other hand, the electron injection layer and the hole injection layer may be made of a material of Si, GaAs, GaN, InP, or SiC, and said quantum well layer may be made of a material of SiGe, InGaAs, InGaN, or InAsP.
Both the electron injection layer and the hole injection layer may use the direct transition type semiconductor and the indirect transition type semiconductor, and the structure that the hole injection layer is located in the lower portion and the electron injection layer is located in the upper portion may be used. The quantum well layer may use the undoped direct transition type and the indirect transition type semiconductors. The external nano dot may use the direct transition type and indirect transition type semiconductors. However, the active layer, that is, the internal nano dot for performing the light emission and the light reception uses the direct transition type semiconductor. The external nano dot and the quantum well layer spatially restrain the carriers such as the electron and the hole to concentrate the carriers into the direct transition type internal nano dot. Also, the external nano dot having a small resistivity allows the carriers to flow through the nano dots, the current by the injection of the minority carrier which the current flows into the non-radiative recombination path is minimized, when the forward voltage is applied to the PN junction made of the hetero junction.